A couple more cold nights this Christmas weekend, then Star Valley will see a change in the weather pattern the last week of 2011. As an illustration of how cold a month it has been thus far, Thayne Elementary has dropped below zero on 18 of the first 23 days of December, hitting a low of -15 on Friday morning. At the official observing site in Afton it dipped to -17 Friday morning with the temperature only rising to 3 above on a sunny afternoon. The strong inversion which has been dominant much of the month was very pronounced again on Friday. As an example Star Valley Ranch reached a high of 20 above around 10am. However the cold air over the valley deepened dropping the temperature to under 10 above by noon where it remained the rest of the afternoon.
Across the Salt Range at the Box Y Ranch after a morning low of 5 below the afternoon maximum was 27 above. The inversion in the narrow Grays River Valley is typically weaker than over the Salt and the mid winter sun can still provide good warming.
High pressure will assure Star Valley if not still cold, a beautifully clear Christmas weekend. With the fresh 2-3 inches of snow on Thursday, a White Christmas will prevail.
The expected major pattern change still looks on schedule for the final week of 2011. The storm track along with a moist westerly flow off the Pacific Ocean will become an increasing factor through next week. If nothing else the cold nights should come to an end by mid-week if not before as clouds provide a blanket over the valley.
|300 mb Forecast Thursday Evening 12/29 2011|
While the core of the strong polar jet should remain somewhat north of Star Valley, the moist westerly flow should provide periods of snow in the mountains and some snow or even rain in the valleys beginning mid week.
The model forecast of precipitation for this next week through Thursday suggest potential for significant snowfall in the mountains of Northwestern Wyoming, possibly as far south as Star Valley.
|Model forecasted Precipitation Through Thursday evening 12/29/11|